As an optical semiconductor device on which a light emitting diode (LED) is mounted, an optical semiconductor device disclosed in PTL 1 has been known. In the optical semiconductor device described in PTL 1, a blue LED is bonded to a molding, the molding is raised to surround the blue LED, the molding is used as a reflection plate to reflect light emitted from the blue LED, a transparent sealing portion containing a fluorescent material is filled into the molding, and the blue LED is sealed.